SKELETON OF UPPER LIMB. 



163 



ture which it seemingly is, really represents some elements 

 which properly belong to the coracoid, and other elements 

 which may greatly increase both in size and complexiiy 

 in other animals. At the same time its inconstancy is 

 such that it may utterly abort, while the scapula and even 

 the coracoid element are largely developed. 



13. That important bone of the human skeleton, the 

 HUMERUS, is constantly present in Vertebrates above Fishes, 

 wherever there is an upper limb at all, although differing 

 in size and shape. It never, however, 

 seems to be present where there is no 

 representative of the hand in this 

 respect, as we shall see, differing from 

 the thighbone in the relation of the 

 latter to the foot. 



In the lowest Vertebrates, i.e. in all 

 Fishes, it is difficult to say what cer- 

 tainly corresponds with the humerus 

 of man, but very probably the several 

 bones or cartilages which articulate 

 with the coracoid and scapula (at the 

 several glenoid surfaces before de- 

 scribed) may be such representatives. 



In this case it may be said (i) either 

 that several (two to five) bones or carti- 

 lages together represent man's humerus, 

 or (2) that each of these is in fact a rudi- 

 mentary humerus, so that a fish has 

 thus several humeri on each side. It 

 is possible, however, that this bone (or 

 perhaps the next limb segment radius 

 and ulna) may be represented by a 

 single cartilage as in Ceratodus, 



Leaving, however, these members of 



- The large upper piece articu- 



FIG 



39. CARTILAGINOUS 

 SKELETON OF A LIMB OF 

 Ceratodus. (After Giin- 

 ther. ) 



the lowest Vertebrate class, w^e shall jates with the "limb root. 



find that higher forms show the several 



parts of man's humerus to be capable of different degrees of 



development, yet that on the whole great variations are 



rare. 



As being the largest bone of the arm the humerus of man 

 follows the general rule, but it may be much exceeded in size 

 by a bone of the fore-arm, as in the Bat and Eagle, while 

 its length may be quite insignificant compared with that 

 of the entire limb, as in the Dolphin. Its length may, hovv- 

 M 2 



